This document claims benefit of priority under 35 U.S.C. xc2xa7120 to Japanese Patent Applications Nos. JPAP 11-252507 and JPAP 2000-195724 respectively filed in the Japanese Patent Office on Sep. 7, 1999, and on Jul. 29, 2000, the entire contents of which are hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to a photomask employed for manufacturing a micro-machine, a microlens, etc., a photomask designing method, a photomask designing apparatus, and a computer readable storage medium.
The present invention further relates to a photoresist manufactured by use of the photomask, photosensitive resin, a base plate microlens, and an optical element.
2. Discussion of the Background
In order to use a photomask for manufacturing a miniature optical element, a technology has been developed in which a three-dimensional-shaped resist pattern as a replica is formed on a photoresist piled on a base material to be mechanically processed, and the base material is etched in accordance with the resist pattern, and thereby the base material can be processed in the same pattern as the resist pattern as the replica. For example, such technology has been already disclosed in Japanese Laid-open Patent Publication Nos. 7-63904, 8-21908, and 8-504515.
Regarding the method of making the complicated three-dimensional form by use of the photoresist, a method of giving the distribution of the light transmission factor to the photomask and controlling the depth of exposing the photoresist has been already studied. As to such a method as mentioned above, some controlling methods have been proposed; namely, a method of controlling the light transmission factor by forming a semi-transparent thin film on the photomask and a method of controlling the intensity of the transmitted light by arranging a large number of fine opening patterns and changing the square measure of the openings. In particular, according to the method of arranging a large number of fine opening patterns, the desired three-dimensional form can be made with the same method as that of mechanically processing the photomask usually employed for a semiconductor, etc. Therefore, the method can be practiced comparatively easily.
Japanese Laid-open Patent Publication No. 8-504515 discloses a system in which a photoresist is laminated on a base material to be processed as a lens, the lens desired to be formed on the base material is divided into fine plural areas, the distribution of the light transmission factor is given to the photomask in accordance with the thickness of the lens in the respective areas, and a desired three dimensional form is formed on the remaining film thickness of the photoresist exposed through the photomask. In the above laid-open patent application, the distribution of the light transmission factor is given to the photomask by the change of the opening rate in the fine area. Namely, the method of arranging a large number of fine opening patterns on the photomask and changing the square measure of the openings, and thereby controlling the intensity of the transmitted light, has been already adopted. An example of a resist pattern 102 formed by use of a photomask 101 is schematically shown in FIG. 16.
Furthermore, the article xe2x80x9cDevelopment of the dispersible microlensxe2x80x9d, Pure Appl. Opt. 3 (1994) 97-101, drafted by the same inventor as that of the Japanese Laid-open 8-504515 discloses that the fine area on the mask pattern is represented by the gray scale pattern 103 represented as an example as shown in FIGS. 17A through 17D. For instance, in the case of expressing 256 halftones, the gray scale pattern 103 of the 256 halftones is previously prepared, the data of the resist depth for the photoresist are taken per each gray scale pattern 103, and the relationship between the gray scale value and the resist depth is stored in a predetermined storage area. Refer to FIG. 18. And then, the photoresist is laminated on the base material to be processed as the lens, and the lens formed on the base material is divided into the fine plural areas. When the distribution of the light transmission factor is given to the photomask in accordance with the thickness of the lens in the respective areas, the gray scale pattern 103 having the gray scale value obtained from the graph of FIG. 16 is selected in accordance with the resist depth which is intended to be formed on the photoresist per each fine area.
According to the background arts, for instance, the arts disclosed in the background-art documents Japanese Laid-open Patent Publication Nos. 7-63904, 8-21908, and 8-504515, and other relevant documents, there exists no advantageous functional effect for improving the above-mentioned photomask design and storage medium.
The present invention has been made in view of the above-discussed and other problems and addresses the above-mentioned defects and troublesome matters of the background arts.
To state in more detail, when a complicated three-dimensional form is made by use of the photoresist, a large number of fine opening patterns are arranged on the photomask and the square measure of the openings is changed, and thereby the intensity of the transmitted light is controlled. Such a method has been already proposed, as mentioned before, as one of the methods of controlling the depth of exposing the photoresist by giving the distribution of the light transmission factor to the photomask. Moreover, as further mentioned before, the method of employing the graph showing the relationship between the gray scale value and the resist depth as exemplarily shown in FIG. 18 has been already proposed as the method of controlling the intensity of the transmitted light.
However, as is apparent from the graph of FIG. 18, even though the gray scale value is 256 halftones for example, since the resist depth is 0 (zero) in a part of the halftones, that is, a part of 0-70 halftones in the graph of FIG. 18, the number of the halftones capable of being used in practice turns out to reduced. That is a problem to be solved. In addition, as shown in the graph of FIG. 18, since the variation of the resist depth for the gray scale value variation is large in the area of about 70-120 halftones, the resolution is lowered in that area. That is another problem to be solved.
Here, in order to increase the number of the usable halftones, it can be thought that the graph of the relationship between the gray scale value and the resist depth as shown in FIG. 18 corresponds to the resist depth. However, on this occasion, a graph has to be made again on the basis of the graph as shown in FIG. 18 every time the depth of the resist pattern to be formed on the photoresist is changed to another value. Furthermore, when the type of the employed photoresist is changed, and even if equal light intensity is given to the photoresist, the resist depth changes. For this reason, even on this occasion, the graph as shown in FIG. 18 has to be made again. In such a situation, the work of making again the graph signifies the necessity of taking again the basic data; those are, the data of the resist depth for the photoresist per each of the respective gray scale pattern 103. Therefore, the work of making the graph turns out to become very troublesome.
A primary object of the present invention is to easily design intensity of transmission light in a fine pattern of the photomask even though the depth of the desired photoresist pattern and the type of the photoresist are changed.
Another object of the present invention is to enable creating the three-dimensional resist pattern with the accuracy corresponding to the number of halftones of the transmission factor arranged on the photomask.